1. Field of the Invention
the present invention relates to a method for accurately measuring resistance to a slippage of rubber employed as tread rubber for use in an automobile tire.
2. Disclosure of the Prior Art
It is heretofore been well known to use a pendulum type apparatus for measuring resistance to slippage as a simple method for measuring coefficient of friction with a dry road surface or a wet road surface. This conventional method for measuring resistance to slippage comprises the steps of mounting a sample of rubber at the bottom of a pendulum, dropping the pendulum freely from a horizontal position and oscillating it, sliding the sample of rubber with respect to a plate similar to a road surface at a lower end position of the pendulum with a certain pressure, measuring the extent of upward movement of the pendulum thereby obtaining energy loss due to sliding friction between the sample of rubber and the road surface-like plate. Thus, rubber's resistance to slippage can be very simply measured.
It is certain that measurement of resistance to slippage can be simply performed with the mentioned conventional pendulum type apparatus of simple construction. But when comparing a value obtained by means of the apparatus with a result of measurement of resistance to slippage of a tire obtained by actually driving it on wet road and dry road, the tire being made of a tread rubber composed of the same rubber as the mentioned sample rubber, it is recognized that there is a relatively reasonable positive corelation therebetween in the aspect of wet road surface test, but that there is substantially no such correlation in the aspect of dry road surface test. As a result, a problem exists in that the mentioned conventional method for measuring resistance to slippage using the measuring apparatus with a pendulum is useful only for the evaluation of resistance to slippage on wet road surface, and is not useful for evaluation of resistance to slippage on dry road surface.